Reductive ring closure methodology toward heteroacenes bearing a dihydropyrrolo[3,2-b]pyrrole core: scope and limitation.

A newly developed reductive ring closure methodology to heteroacenes bearing a dihydropyrrolo[3,2-b]pyrrole core was systematically studied for its scope and limitation. The methodology involves (i) the cyclization of an o-aminobenzoic acid ester derivative to give an eight-membered cyclic dilactam, and (ii) the conversion of the dilactams into the corresponding diimidoyl chloride, which undergoes (iii) reductive ring closure to install the dihydropyrrolo[3,2-b]pyrrole core. The first step of the methodology plays the key role due to its substrate limitation, which suffers from the competition of oligomerization and hydrolysis. All the dilactams could successfully convert to the corresponding diimidoyl chlorides, most of which succeeded to give the dihydropyrrolo[3,2-b]pyrrole core. The influence of the substituents and the elongation of conjugated length on the photophysical properties of the obtained heteroacenes were then investigated systematically using UV-vis spectroscopy and cyclic voltammetry. It was found that chlorination and fluorination had quite a different effect on the photophysical properties of the heteroacene, and the ring fusing pattern also had a drastic influence on the band gap of the heteroacene. The successful preparation of a series of heteroacenes bearing a dihydropyrrolo[3,2-b]pyrrole core would provide a wide variety of candidates for further fabrication of organic field-effect transistor devices.

Fluorescent gold nanoparticles: synthesis of composite materials of two-component disulfide gels and gold nanoparticles.

Pseudoenantiomeric ethynylhelicene oligomers containing a disulfide group formed two-component gels, which showed different solvent properties from gels without the disulfide group. The disulfide gels reacted with gold nanoparticles, and the resulting organic-inorganic composite materials exhibited fluorescence emission between 600-800 nm, along with emission from the oligomers at 450 nm. The disulfide gels and isolated gold nanoparticles loaded with the oligomers did not show the former emission. The 600-800 nm emission reversibly disappeared upon sol formation with heating, which was accompanied by an enhancement of the emission at 450 nm. The novel emission was also observed in the solid state.

Two types of two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers.

Two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers in toluene exhibited two different properties depending on difference in numbers of helicenes in the two components. The combinations (M)-5/(P)-4, (M)-6/(P)-4, and (M)-7/(P)-4, which contained oligomers with comparable numbers of helicenes, formed transparent gels (Type I gels). The combinations (M)-6/(P)-3, (M)-7/(P)-3, and (M)-8/(P)-3, which contained oligomers with considerably different numbers of helicenes, formed turbid gels (Type II gels). Negative Cotton effects were observed for the Type I gels in the region between 350 and 450 nm, and were positive for the Type II gels, despite the use of (M)-oligomers for the longer components. UV/vis exhibited absorption maxima at 350 nm for the Type I gels and at 338 nm for the Type II gels. Different behaviors in gel formation processes were observed by fluorescence studies. Atomic force microscopy analysis showed fiber structures of 25-50 nm diameter for Type I gels and bundles of 100-150 nm diameter for Type II gels. The stoichiometry in gel formation also differed: The Type I gels showed 1:1 stoichiometry of the two components; the Type II gels showed no 1:1 stoichiometry, likely 1:2 stoichiometry. Using the Type I and II gels, two-layer gel systems were constructed.

Benzo[f]benzo[5,6]indolo[3,2-b]indole: a stable unsubstituted 4nπ-electron acene with an antiaromatic 1,4-diazapentalene core.

A stable unsubstituted 4nπ-electron acene with an antiaromatic 1,4-diazapentalene core was prepared via an unprecedented mild oxidation. Further investigation showed that the stability of such acenes was dependent on the fusion patterns of the peripheryl benzene rings to the centre core.

Chiral recognition in aggregation of gold nanoparticles grafted with helicenes.

Chiral recognition was observed in the interactions of gold nanoparticles grafted with (±)-, (M)-, and (P)-helicenethiol. Although the nanoparticles contain equal enantiomeric excess, a 1:1 mixture of (M)- and (P)-nanoparticles aggregated more rapidly in solution than (±)-nanoparticles.

Optical resolution of aromatic alcohols using silica nanoparticles grafted with helicene.

Optically active silica nanoparticles, with a 70-nm diameter, grafted with (P)-1,12-dimethyl-8-methoxycarbonylbenzo[c]phenanthrene-5-carboxyamide were synthesized, and their use in the kinetic resolution of aromatic alcohols was examined. Up to 61% ee for (S)-2,2-dimethyl-1-phenyl-1-propanol was obtained by a preferential precipitation of aggregates formed with (P)-nanoparticles.

Quinone tailored selective oxidation of methane over palladium catalyst with molecular oxygen as an oxidant.

With the in situ generated H(2)O(2) tailored by the addition of p-tetrachlorobenzoquinone, the product can be effectively steered towards either HCOOH or the methanol derivative CF(3)COOCH(3) during the direct oxidation of methane with molecular oxygen over palladium catalyst.

Combined redox couples for catalytic oxidation of methane by dioxygen at low temperatures.

The combination of three redox couples Pd2+/Pd0-quinone/hydroquinone-NO2/NO creates an electron-transfer loop, which facilitates one-pot catalytic oxidation of methane selectively to methanol by dioxygen in CF3COOH at a temperature as low as 80 degrees C. This is the first example where an organic cocatalyst significantly increases the catalytic efficiency of a transition metal in the selective oxidation of methane in the presence of dioxygen.